Since 2007, the number of households are paying more than half of their income for housing despite the crash in home values and bottom basement interest rates has increased by 2.6 million.

As of 2011, over 40 million households were at least moderately cost burdened (paying more than 30 percent of their incomes for housing), including 20.6 million households that were severely burdened (paying more than half of their incomes for housing), according to the State of the Nation’s Housing 2013 released yesterday by the Joint Center for Housing Studies at Harvard University.

The latest increases in the number of severely burdened households represent a jump of 347,000 from 2010, 2.6 million from 2007 when the recession began, and 6.7 million from a decade ago.

The most recent increases were almost entirely among severely burdened renters, whose numbers soared by 2.5 million from 2007 to 2011, pushing the share to 27.6 percent. While up only 173,000 over this period, the number of cost-burdened homeowners had already surged by 2.7 million in 2001-07 amid the sharp rise in house prices and the widespread availability of easy mortgage credit.

However, the incidence of cost burdens has not fallen much more dramatically among owners despite the substantial decline in home prices and low interest rates. Indeed, the share of severely burdened owners rose from 12.1 percent in 2007 to 12.6 percent in 2011. The lack of progress reflects the difficulties that many owners locked into excessive mortgage debt face in attempting to refinance and the still-weak state of the economy. In fact, the overwhelming majority of underwater homeowners continue to make payments on mortgages that exceed the present value of their homes, the report said.

While increasingly prevalent at all income levels, severe hous­ing cost burdens are much more common among households with the lowest incomes. Nearly seven out of ten households with annual incomes of less than $15,000 (roughly equivalent to year-round employment at the minimum wage) are severely burdened. With income inequality worsening over the past decade, the share of households with these low incomes has continued to grow.

Meanwhile, the stock of low-cost housing that these households can afford continues to shrink. Between 2007 and 2011, the number of renter households with extremely low incomes (less than 30 percent of area medians) increased by 2.5 million. Over the same period, the number of available housing units that households at this income level could afford to rent declined by 135,000. As a result, the gap between the supply of affordable housing and demand from extremely low-income renters dou­bled in just four years to 5.3 million units. Given that the typical unit completed in 2012 rented for $1,100 per month, new hous­ing development is unlikely to alleviate this affordability gap.

The dramatic increase in the burden of housing costs was one of a number of topics discussed at a webinar that originated at the Center’s offices in Cambridge.

Despite Lower Prices, 40 Million Households are Burdened by Housing Costs | RealEstateEconomyWatch.com.